Electric discharge device and method of fabrication



Apri 23, 1946. T. G. CRAWFORD ELECTRIC DISCHARGE DEVIGE-AND METHOD oF EABRICATION 2 Sheets-Sheet l Filed Feb. l2, 1943 Inventor: Thomas G. Crawford.,

bg WWM! His Attorneg.

ELECTRIC DISCHARGE DEVICE AND METHOD OF FABRICATION Inventor:

v Thomas G. Crawford, I

His Attorneg.

Patented Apr. 23, 1946 ELECTRIC DISCHARGE DEVICE AND s METHOD E FABEICATIQN -Thomas G. Crawford, Glenville,-N. Y.,-assignor to I GeneralA Electric Company, a corporation of New YorkV Application Februaryl, 1943, Serial No. .47517526 (Cl. Z50-2725) 9 Claims.

My inventionV relates to electric discharge devices and methods of ,fabrication thereof, and more particularly Ato electric dischargedevices of the high vacuum type employing thermionic cathodespeculiarly adaptable for operation at high voltage and current. l

It has been appreciated for some time that it is desirable in-electric discharge devices of the high vacuum type to employ materials for the thermionic cathodes thereof which are readily capable of supplying the requisite amount of current and which are not subjected to inordinate rates ofv deterioration due to oxidation or disintegration by ionic bombardment. For example, in United States Letters Patent No. 1,529,597,

granted March 10, 1925, upon an application of Irving Langmuinthere is disclosed a method for the carbonization of thoriated tungsten filaments whereby the ypresem'ze of carbon indefinitely limitedfamountsfprevents not only reoxidation of the active thorium material but also Ybeneficially reduces thoria to the active state.. In accordance with the teachings of my invention described hereinafter, I provide Ynew and improved'. structures forelectric discharge devices, and methods of manufacture or preparation, whereby the electric discharge devices are capableof meeting severe load requirements such as high voltage and current conditions, and wherein the structure and method of manufacture are peculiarly adaptable to factory methods and procedure.

g It islan object of my invention to provide new andv improved electric discharge devices. It is another vobject of my invention to provide new and improved methods of manufactur- Vingor fabricating electric discharge devices of the hightvacuum type. i

It is a further object of myv invention to provide new and improved methods of precarboniz ing filamentary elementsor cathodes such as thoriated tungsten cathodes forhigh vacuum elec.. tric discharge devices. C, i

slt is a still further object of my invention to provide new and improved'electric discharge devices comprising a plurality of individually or separately precarbonized lamentary Vcathodeelements which are intended for use in' high vacuum electric discharge devices and which comprise structure forv equalizing the potential difference across'the diierent cathode elements. v I Y It is a still further object ofnmy invention to provide new and improved methods of pre-carbonizing lamentary cathode elements for high vacuum electric discharge devices vand 4which afford numerous advantages, some of which include uniformity of resistancev ofthe `respective elements, .substantial freedom from free carbon delposits in inaccessible places, constant or uniform filament resistance, avoidance of the requirement of subjecting the electrode amounts generally to the lhigh ashing temperatures previously required, and the incident reduction in strains produced on the electrode mount.

Briefly stated, in accordance with one'of the illustrated embodiments of my invention I p rovide a new and improved electric discharge de-v vice of the highvacuum type wherein a thermionic cathode comprises a plurality of lamentary cathode elements'of hairpin configuration which have been individually precarbom'zred and which are supported in theA desired spaced relation with respect to.. an associatedanodeby means of an electrode .mount or stem construction which not only supplies current toadjacent individualpairs of elements in series fromvwexternally accessible terminals, vbut also affords ready. means forequalizing thepotentials of the common junctures of adjacentL pairs of the lamentaryrcathode elements. In thisl modification of my invention means are also provided for engaging the closed ends of the lamentary elements to maintain these elements in the desired positions, and comprises an anchor` plate assembly which is spring biased to exert a desired longitudinal or axial force on the elements. Y

" In a further modification of my invention, the lamentary cathode comprises a pair of oppositely wound lamentary cathode elements of helical conguration which are supported by lead-in conductors attached to the stemconstruction and which are weldedv thereto. An equalizingvlead-V in conductor is'A employed between the common juncture of the helical elements so that the potential of the vcathode elements and the electron emission therefrom may be equalized. e Y

In accordance with a still further feature of myinvention, I provide-new and improved methods i of nprecarioionizing thoriated tungsten filamentsinorder to 'selectvfor use in afparticular electric discharge deviceiilaments ofl uniform resistance.y The lamentary cathode elements are heated in a hydrocarb'onvor carbonaceousI atmosphere to a temperature of substantially 2500 or 2700 C. for a period of time ranging from 20 to seconds to eiectthe carbonization of the thoriated tungsten of the elements. The elements are then permitted to cool and the resistances thereof aremeasured fortth'e purpose of Vselecting `those elementsV having-'substantially equal or uniform resistances. The selected .elements are then For a better understanding of myninventicm,V

reference mayr be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. 1 illustrates in general outline the type of electric discharge device to which r my invention may be applied and shows the enclosing envelope partially broken away and the enclosed electrode structure includingfthe. ila-k Figa mentary cathode and the gridv structure. illustrates in enlarged form the stem construction including the supported cathode and grid. Fig. 3 illustrates an alternative embodiment wherein the lamentary cathode comprises a pair of oppositely wound helical elements supported from the stem construction.

Referring now to Fig. 1 of the drawings, I have there illustrated my invention as applied to a high power transmitting electric discharge device which includes an externally cooled anode IA of tubular coniguration which is closed at one end and which merges at its other end into a reversely bent portion 2. The edge of the latter portion is sealed to a glass bulb 3 which, in turn, issealed to a vitreous part of the stem construction 4. The anode 2, the'glass bulb 3 and the stem construction 4 constitute in combination a vacuum-tight envelope of the electric discharge device. A angedrmember 5 joinedto the reversely bent anode portion 'serves duringuse of the tubeto support the tube or eletricdischarge device envelope and `'to connectfit with a cooling packet (not shown) for the anode.'

At its upper end, thel glass bulb 3` terminates in a dat vitreous cap 6 which supports-La plurality of externally accessible terminals or terminal posts'-l inclusive','only three of which are shown in Fig. l. Each of these terminal. posts may comprise a cup-like member comprising an elongated tubular portion anda relatively large end portion, these parts being respectively supported by and sealed to the vitreous part of the stem construction ci, The details of the electrode construction, and particularly the iilamentary cathode and grid structure, may 'be more fully appreciated by referring to Fig. 2.

The electrode mount and stem construction shown in the enlargedview of Fig. 2 comprises vitreous part 6 Which is sealed at l I to the glass envelope 3 shown in Fig. l. I provid-ea thrmionic cathode comprising a plurality of filamentary elements which may have a hairpin configuration and which are centrally positioned Within the metal anode l. For example, IY provide a plurality of hair-pin iilamentarycathcde elements iarranged annula'rly, thereby `forming asymmetrical mesh of electronemissivesurfaces; Onlyelements lil-I8 are illustrated inFig.` 2 and it Will be appreciated that other elements, not shown, complete the electron emissive structure of the cathode;

I providel means supported by and attached to the stem construction ll'for supporting the lamentary cathode' elements l2-I8 in spaced relation Within the anodel, and also in spaced relation with respect to grid structure-to be described presently. Mcrep'articularly, I provide a pair of metallic plates or disks I9 and 20 which are spaced and electrically insulated, and which are respectively connected to terminal posts 'I and 8 through rigid conductors 2l and 22. A plurality of rigid metallic connectors 23-28, inclusive, are employed to connect one open end of each adjacent pair of. elements i248, respectivelmto plates 4I9 and '20j so that adjacent pairs .may be energized in series relation from a source connected to terminal posts l and 8. For example, elements I4 and l5 are connected in series relation through connectors 2li and 25, the former of which is connected to plate I9 and the latter of which is connected to plate 2B. In like manner, other pairs of thefilamentary .cathode elements are connected to plates l'- and29. In this manner, the rilamentaryrheating elements are energized in a parallel-series relationship, that is the various individual pairs of serially connected elements are energized in parallel.

' I also employ means for joiningthe other open ends of adjacent pairs ofthe lamentary heating elements and for Yeuualizing the potentials of the common junctures of adjacent pairs. This means may take the form of a metallic plate 28 spaced and electrically insulated from plates I9 and .2B and which supports a plurality of connectors 30-32 which are conductively connected to plate 29 and to which the cathode elements are welded. Y In order to provide a rigid mechanical construction, as well as the requisite electrical insulation, I provide a plurality of tubular insulators which extend through various appropriate plates and receive `the connectors 2 3-2B and connectors 30f32. For example, suitable insulatorsl sueltas quartzinsulators 33 and 34, extend through apertures 35 in. plates i9 and 29, thereby insulating connectors 23'and 21 therefrom. Similarly, tubular vitreous or quartz insulators 36 and 13,? extend through apertures in plate 2B and insulate connectors therefrom. I Insulators 33, 3ft, 3E and 3 1, which are merely representative of the plurality of insulators SQ employed, may be constructed, as illustrated, to allord appreciable shoulders which' permit accurate and firm spacing of plates I9, 26a-nd 2,9. l

At the lower end of the cathode structure, I provide an anchor plate assembly whichserves to maintain the filamentary. cathodeelements in the desired rigid spaced relation With respect. to the other electrodes ofthe discharge device. The anchor plate assembly comprises a metallic plate 38 which supports a plurality of annularly spaced retaining members, such as hooks 39, which are insulated from plate 38 by means o'faplu'rality of individual insulators 40 preferably'constructed of quartz. f I. As a means for iirmly positioning thel anchor plate assembly, I provide an axial or longitudinal rod 4l which is attached toplate 38 atitslovver extremity and which is'supportedfr'om plate '20. I also provide means forexerting an axial or lon-l gitudinal force Qn' rod 4l toiirmly position the anchor plate assembly and, in turn, exert. a longitudinal` or axial force on the i'ilamentarycathode elements. lZ-iil, This means may be of resilient character comprising a compression Spring 42 which engages a bushing c3 provided with a vshoulder adapted to receive the upper extremity of the electric discharge device.

Part 46 which 1n turn, supnortsa pluralityof vertical-1 or longitudinal conductors 4l and 48 which Serve as support orrositicnins members fora helically wound grid'49. LThe lower ends of the vertical conductors 41 and 48 maybe closed byametalcap.

Plate'45, which supports the above described grid-structure, may be attachedtoapair .of rigid conductors IX and 52 which are respectively coninectedto-terminal posts 9 and I0. If desired, a single grid supporting conductor anda single terminal post may be employed. l v. The 'individual filamentary cathode elements, of whichy elements'I2-I8 are representative, are pre-carbonizedbefore mounting' or assembling" in the structureshown in VFig. 2'.. Theseelements are ashedland pre-carbonized, before mountin`g', in van atmosphere of Va, hydrocarbon orlearbonaoeous vapor. For example, the elementsV maybe' supported by a fixture (not shown) positioned within a compartment or chamber to'whichthere is supplied va desired hydrocarbon vapor, suchas a' mixture of benzene and hydrogen, in the proper l proportions to eleet the desired carbonizatioirof the elements within a predetermined interval of time. The temperature of the elements is raised by transmitting through the elements current of a predetermined value to elect the desired carbonizatiom. For example, .thetemperature *of the cathode elements may be raised to a Valuewithin the neighborhood of 2500 to 2700 C. and exposed to the hydrocarbon vapor for a period of time ranging from 25 to 45 seconds. 1- i 'Of course, in carrying out the'method in accordance with my invention time is allowed` for the elements to assume the desired temperature, the `pericd'of time depending u'ponf the size of the elements undergoing treatemnt, the" resistance thereof, andthe current which is transmitted therethrough. 4As an example of the period/oi. time required in the process of flashing and pre-f; carbonizing for a particular sized thoriated tungsten lamentary element, I` have -foundthat a current of 100 amperes should be supplied tothe element andan interval of 30 secondsA allowed for the element to attain the desired ashing and pre-carbonizing temperature. The elements are maintained at that temperature'fora period rof 25'seconds, atA the expiration'of which theele ments are permitted to cool for a period oftime approximating two minutes, whereafter the"`ele. ments may be mounted,V that'iswelded tothe connectors of 'which connectors 23-28,"inc'lusive.' are representative. Of course, prior to Welding to these connectors, the filamentary cathode ele'-v ments are threaded through the eyes provided by hooks 39. l' y As an Vintermediate step before assembly in' the electrode mount shown in Fig. v2, resistances 'of the individual cathode Velements are measured for the purpose of selecting-and using in a particular discharge `device,those elements having substantially the same or uniform-resistances. Inthis manner, the voltage` drop along the lindividual elements is maintained' substantially equal, there-T by making it'possible'to provide a cathodee'mite ting structure wherein the'current emission'from individual elements.'issubstantially uniform'. 'The advantages'of such uniformity in electron ernls'-A sion.- fromia directly heated cathode islwell a'p# preciated, the advantages including increasedli'fe of the cathode structure and improved operation Another advantage incident to the individual precarbonization of the various cathode elements is; the; feature which; permits choice: yof the ele ments to establish small tolerances in resistances simply -by selection.' In this relation, the cathode elementsandthegrid structures, since the cath- .ode elements have been pre-carbonized apart Vfromthe velectrode mount, may be maintained or kept vfree off,extraneous particles and no large quantities of'. free-icarbonv are deposited in inaccessible'places., The presence of extremely large `quantities offfree carbon on the electrode mount,

or on pi'trtsth'ereof',l would cause high voltage gradients and consequently would cause breakdownV at relatively high voltages.

'A still further advantage of apparatus built in accordance with myinvention is that the electrodemountsLwhich are relatively expensive, are not exposed to the high ashingtemperature previously required.l in the manufacture onde'- vices of this character;sinceztheashingfof the cathode elements has been performed apart from the electrode mount. A still further advantage in this connection is that incident to .the same procedure in which theindividual preflashing orcarbonization ofgthe cathode elements doesvnot necessitate the subjectionof the electrode mount to 'great mechanical-strains which,v according lto the prior artarrangements, were present when the elements were' flashed assembled with vand as, parts ofthe electrode mounts. InFig. 3 of the drawings .there is illustrated a furthermodificationiof my invention showing an electrode mount and stem assembly which may be employed in an velectric discharge device of the general configuration' shown in Eig. 1. The stem construction comprises a vitreousv part 53 which maybe sealed to a glass bulb,v such as that shown in Fig. 1, and supports terminal lpostst, 55, and 56 in sealed relationthereto. Terminalposts for the grid structure are not illustrated in this view. Lead-in conductors 51 and 58, of rigid construction, support a 'pair of individually and separately pre-carbonized'cathode heating elements of helical congurationlwhich are oppositely Wound and which together constitute the directly heated cathode of an electric discharge device. A furtherlead-in conductor 6l, which is connected to terminal post 55, extends longitudinally or axially the electrode mount and Vserves as a central supporting'element as Well as an electrical connection to the lower fends of the helical elements 592116 ill-,

e In the assembly operation, elements 5e and 60 maybe boundto lead-in conductors 51 and 58 by meansofj refractory. binding wires 62 and E3 and, jin likemanner, the lower ends of elements 59,.,and 60 `may .be bound -lto conductor 6I and to each other by means .of a refractory binding wire 64. After assembly, the elements 59r and 60 may be arcwelded at places indicated by numerals 65, 56'A and `61 toestablsh low resistance electrical connections-between the-elements and the varieL ous lead-in'conductors. -'A4 helical gridv68-is supported from a flanged cylinder 69fWhich',jin turn, `is-supported by cori-Y ductors v'lll'andglL eithervof which, 'or both of which, mayj be connectedfto terminal posts `not shown. The helical grid 68 is maintained in the desiredposition by means of a plurality of longitudinal orvertical conductors 12. Y

Helical cathode elements 59 and S0 may also be flashed or pre-carbonized in accordance .with the above described method and after pre-carbonization may fbe `assembled as parts of the electrode mount. The advantages ofthe above described method also apply to the construction shown in Fig. 3. l

In the foregoing specification and in the` appended claims the word pre-carbonized" is employed to designate elements that are carbonized prior to the time that they are secured to an electrode mounting or stem mountingl which forms a part or the discharge device as distinguished from the usual construction in which the cathode elements are secured to the electrode mounting and the mounted elements later carbonized.

While I have shown and described my invention as applied to electric discharge devices of a particular character, it will be obvious to those skilled in the art'that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1.An electric discharge device comprising a plurality of electrodes including a tubular metallic anode constituting a portion of an enclosing envelope, a stem construction comprising a vitreous part sealed to said anode, means supported by said stem construction for maintaining a lamentary cathode in spaced relation within said anode and comprising a pair of spaoedand electrically insulated plates connected to. externally accessible terminals, a plurality of annularly spaced filamentary cathode elementsof hairpin configuration electrically connected to said plates, an anchor plate engagingV said elements at the closed ends thereof, and a rigid spacing rod extending longitudinally said cathode for exerting a longitudinal force on said anchor plate thereby retaining said lamentary cathode elements in position.

2. An electrick discharge dev-ice comprising a plurality of electrodes including an elongated tubular anode, a stem construction comprising a vitreous part sealed to said anode, a thermionic cathode comprising a plurality of hairpin-type elements, means supported by said Stem construction for maintaining said elements in spaced relation with each other and with respect to said anode comprising a pail` of spaced andelectrically insulated plates connected to externally accessible terminals, a plurality of annularly spaced rigid connectors for connecting said elements to said plates, an anchor plate assembly supported from said stem for exerting a longitudinal force on said elements and for retaining Said elements in position, and resilient means supported by said stem construction for maintaining said plate assembly in position.

3. An electric discharge device comprising a plurality of electrodes including an anode and a thermionic cathode including a plurality of lamentary hairpin-type elements, a pairof spaced metallic plates electrically connected to externally accessible terminals and a third metallic plate spaced and electrically insulated from said pair of plates, a metallic supporting member for connecting ends of two adjacent filamentary elements to said third plate, and a pair of filament supports connected respectively to the remaining ends of said elements and to said pair of spaced metallic plates whereby said two elements are energized in series.

4. An `electric discharge device comprising a plurality of electrodes including an anode and a asaaom thermionie cathode comprising a plurality ci lfamentary hairpin-type elements,v` a mount f'or supporting said elements and comprising a pair of substantially vparallel metallic plates spaced apart and connected to externally accessible terminals, a third metallic plate spaced from said pair :of plates, a rigid connector for joining ends of pairs of adjacent lamentary elements, and a pair of rigid connectors respectively connected to the remaining ends of said pair. of elements and said pair of plates whereby said elements are energized in a parallel-series relationship.

5. An electric discharge device comprising a plurality of electrodes including an anode and a thermionic cathode comprising a plurality of filamentary hairpintype elements, a mount for supporting said elements and comprising means for energizing adjacent pairs of filaments in see ries including a p air of spaced metallic plates connected to externally accessible terminals and a third plate spaced and electrically insulated fromsaid pair ofplates, a filament connector electrically connected to ends of adjacent filamentary elements, and a pair of rigid filament con-- nectors respectively connected to the remaining ends of said adjacent pair of elements and con-v nected to said pair of plates.

6. An electric discharge device comprising a plurality'of electrodes including a tubular anode surrounding a thermionic cathode comprisinga pluralityv of filamentary hairpinetype elements, a pair of spaced and electrically insulated plates respectively connected tov externally accessible terminals, a. third plate electrically insulated from said pair of plates, and a plurality ofl rigid annularly spaced filament connectors for energizing adjacent pairs of elements in series whereby ends of adjacent elements are connected to said third plate and the remaining ends, of adjacent pairs are respectively connected to said pair ofplates. e

7. An electric discharge devicey comprising a plurality of electrodes including an anode and a, thermionic cathode comprising a plurality of annularly spacedl llamentary elements of hairpin configuration, a stem construction for sup'- porting said elements and comprising a pair of spaced and electrically insulated plates connected to externally accessible terminals, means supported by said plates and respectively connected to ends` of adjacent elements for supplying current thereto, and means for equalizing'the poten- Ytial of common junctures of adjacent pairs of elements comprising a third plate connected to the remaining ends of adjacent pairs of ele-V ments.

8. An electric discharge device comprising a Y plurality oi?V electrodes including a tubular Inetallic anode constituting a portion of an enclosing envelope, a stem construction comprising a vitreous part sealed to said anode, a thermionic cathode comprising a plurality of llamentary elements of hairpin configuration annularly arranged within and spaced from said anode, means for energizing said elementscomprising a pair of spaced and electrically insulated plates supported by said stem construction and connected to Vexternally accessible terminals, a plu: rality of pairs of rigid connectors supported by said plates and connected individually to ends of adjacent pairs of elements, a third plate dise placed from said pair of platesv and electrically insulated therefrom and supporting a plurality of rigid connectors each connected. to. remaining ends of adjacent pairs of elements thereby serve ing as potential equalizing means for the common junctures of adjacent pairs, an anchor plate assembly provided with a plurality of annularly spaced hooks engaging the closed ends of said elements, a longitudinal spacing rod supported by said stem construction for exerting a longitudinal force on said annular plate assembly, and resilient means for exerting a longitudinal force on said rod.

9. An electric discharge device comprising a plurality of electrodes including a tubular metallic anode constituting a portion of an enclosing envelope, a stem construction comprising a vitreous part sealed to said anode, a thermionic cathode Within said anode and comprising a plurality of annularly spaced lamentary elements of hairpin configuration, means for supporting said catho'de and supplying current thereto comprising a pair of spaced and electrically insulated plates attached to said stem construction and comprising a plurality of pairs of rigid connectors for respectively connecting ends of adjacent pairs of elements to said plates, means for connecting adjacent pairs of elements in series reing rod between said stem construction and said anchor plate assembly for exerting a longitudinal force on said plate assembly thereby retaining said elements in the desired positions, and means comprising a compression spring mounted on one of said pair of plates for exerting a longitudinal force on said rod.

THOMAS G. CRAWFORD. 

